The present invention is related to apparatus for controlling the feeding of elongated lengths of bar stock, metallic or non-metallic, to the cutting head of a CNC machine center or other type of lathe. Contemporary machine shops are increasingly relying on the use of CNC (Computer numerical control) machine centers for a variety of operations. The CNC machine centers are high-speed, demonstrate high levels of accuracy, and are virtually fully automated.
One operation that has remained somewhat problematic, however, is the automatic feeding of bar stock to the center cutting head. Bar stock most frequently is metal and of a length often in excess of eight to ten feet. Most CNC machine centers have a continuous and automatic feed mechanism wherein the bar stock is fed into an inlet in the machine center and then automatically pulled through a feed orifice having an outlet into the cutting head. When the bar stock is not fully controlled or restrained along its length, the free end, which is away from the cutting head, is subject to high levels of vibration manifested by end-whipping or slapping as the stock is turned. Such bar stock is turned at very high speeds, frequently in excess of 5,000 revolutions per minute. Therefore, when vibration of the free end is not controlled, accuracy of the cutting operation is severely affected.
Known attempts to compensate for this vibration problem include apparatus designed to restrain the bar stock during the feeding and turning process. Such apparatus generally is comprised of some type of sleeve or cylinder through which the stock is fed; the inner diameter of the sleeve being reduced to a dimension just larger than the diameter of the bar stock and thus utilized to reduce vibration of the free end of the stock.
Most apparatus which is particularly adapted for CNC machine centers include large, awkward-to-handle feeding tubes having continuous inner diameters generally somewhat greater than the outer diameter of the stock, so that the stock does not contact the tube and create drag. No attempt has previously been made to reduce the inner diameter down to that which is substantially the equivalent of the outer diameter of the stock because the drag created thereby substantially reduces cutting time and accuracy. However, when drag is fully eliminated, vibration resumes.
The present invention is directed to an apparatus which is useful with a variety of types of machine centers and lathes, and which can be easily adapted to feed stock of almost any diameter or length. The apparatus restrains bar stock within very close tolerances and thereby substantially eliminates any vibration or whipping effect. In its simplest embodiment the present invention is a feed means that restrains bar stock, both exteriorly of the machine center and also within the feed orifice which leads up to the cutting head, by means of a restraining sleeve, portions of which are comprised of bushings which have an inner diameter substantially equivalent to the outer diameter of the bar stock which is being cut. Because only relatively short, spaced-apart segments of the restraining sleeve are in contact with the bar stock being fed therethrough, the bar stock is not subjected to the drag effect that slows cutting speed. The bar stock is however, restrained from any vibratory end whipping effect and the rpms can be substantially increased. Thus, both the cutting speed and the accuracy of the cutting are improved.
In the preferred embodiment, a first restraining sleeve is removably positioned in the feed orifice of the CNC machine center to control vibration of the bar stock near the point of cutting. A second restraining sleeve is supported outside the CNC center, in abutting relationship to the inlet to the feed orifice, to control the free end of the bar stock as it is fed into the orifice. Both restraining sleeves and the bushings therein are provided in a variety of sizes in order to accomodate bar stock of various outer diameters.
The second restraining sleeve, supported outside the CNC center, is removably inserted in a support tube that is mounted adjacent the CNC machine center. When the outer diameter of the bar stock changes, the restraining sleeves are selectively exchanged as appropriate by removing the sleeves from the feed orifice and support tube and replacing with sleeves having the appropriate inner diameter. Such changes can be made in very little time and with no affect on the program control of the CNC machine center. Special needle bearing-mounted bushings are substituted for the primary stationery bushings when hexagonal or square bar stock is being cut. The inner wall of these bushings is squared or hexagonally shaped to accept such stock.
In addition to a greatly improved means for feeding bar stock to a machine center, the preferred embodiment of the present invention further provides means for supporting a supply of stock for operation. The details of the structure are outlined below. A study of these details reveals how the primary objective of providing a highly improved means for controlling the feeding of bar stock to a lathe is achieved. Other objectives include the provision of a bar stock feeding apparatus that improves accuracy by elimination of vibration and end-whipping of the stock, without creating excessive drag which slows cutting speed. Other and further advantages will be realized as the following detailed description is studied in conjunction with the accompanying drawings.